THAT'S WHY IT GOES DARK IN THE VIEWER WHEN YOU TAKE THE PICTURE.
Honestly, I have no idea how I didn't realize this, but I always thought it was the shutter closing during a photo that caused it to go dark. No idea why I thought that, because it doesn't make any sense.
I feel like this type of guides are only understood by people who already know how different camera settings affect the picture quality. As a such person it's really difficult to imagine myself in the place of a total novice but I can imagine this not being helpful at all.